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Homework Help: Double slit problem (simple)

  1. Dec 8, 2004 #1
    single slit problem (simple)

    A single slit diffracts laser light of wavelength 610 nm onto a screen 3.25 m away. The distance between the two first-order maxima on either side of the central peak is 3.65 mm. How wide is the slit (in mm)?

    I figured the formula [tex]\lambda m = d sin(\theta)[/tex] would work but it's not. Here's my work:

    sin(theta) = 3.65*0.5*10^-3 / 3.25 (since the angle is really small tan(x)~=sin(x))
    sin(theta) ~= 5.62*10^-4

    610*10^-9*1 = d * 5.62*10^-4

    d~= 1.09mm or 1.09*10^-3m

    This is wrong. What did I do wrong? Thanks
    Last edited by a moderator: Dec 8, 2004
  2. jcsd
  3. Dec 9, 2004 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    Your formula uses the angle between the central peak and the first order MINIMA. That distance is 1/4 of 3.65mm.

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